1. Field of the Invention
The present invention generally relates to drill resistant, hard material, and more particularly relates to a structure which is braised onto a steel plate for resistance to drilling.
2. Background Information
There is often a need to make a surface harder than steel. This often occurs in the drilling industry in which drill bits need to have extreme hardness and the ability to drill through hard materials. Drill casings also need to have a hardened surface so that they have longer wear against other drill casings. The approach to making an abrasive for better cutting of drill bits is to weld onto the drill bits granules of hardened material such as tungsten carbide.
U.S. Pat. No. 5,396,041, to Miller et al. also provides an approach to making a plate hard to drill. The Miller patent utilizes welding by the tungsten inert gas (TIG) process to embed tungsten carbide particles in a steel matrix. This matrix is specifically structured so that the tungsten carbide particles are positioned in a gradient so that the tungsten carbides are most concentrated at a distance away from the surface of the steel plate. However, the resulting steel plate has a smooth surface of steel, in which a drill bit may begin drilling. As the drill bit proceeds through the plate, it encounters hard particles of tungsten carbide, but it also is stabilized against chattering and vibration by the hole which surrounds it. If the hard particles cause the bit to break, another bit can be started in the same hole, and drilling progress can be made. Furthermore, in the TIG process, the plate and the welding rod must be heated to a high temperature. The steel in a localized area is melted, and the steel of a welding rod is also melted and mixes with the molten steel of the plate steel. This leaves a fairly narrow track of welded material. To cover a plate with such weld tracks is time consuming, and the extreme heating of a localized spot causes severe buckling of the plate.
A further drawback to the Miller process is that the finished product has the tungsten particles embedded in the steel matrix, so they are not visible. It is thus impossible to visually inspect the resultant plate for proper dispersion and coverage of the particles in the plate. The temperature during welding is high enough to weaken the strength of the already brittle tungsten carbide particles.
What is needed is a drill resistant hard plate and a method for making same, which uses a temperature lower than welding, and which causes drill bits to shatter before they can began drilling into the hard plate.
These and other objects are accomplished by the resistant hard plate of the current invention. The current invention includes a drill resistant hard plate and a method for making the same.
The method for making the drill resistant hard plate includes a first step of providing a steel base plate. In the broadest form of the invention, the next step is to attach hard particles to the steel base plate. This can be attachment by any material which forms a matrix that binds the hard particles to the steel base plate. This could include a matrix of epoxy, a sufficiently strong adhesive, or molten metal, including solder.
One version of the process of the invention involves using a material which involves molten metal. The next step in this process is to preheat the steel base plate. The next step is applying a brazing material to the preheated steel base plate, so that the steel base plate is covered by the brazing material. The next step is applying a layer of hard particles on the heated and braised steel base plate, so that the hard particles blend with the brazing materials and are bound to the steel base plate. They can also be partially covered with a layer of the brazing material, or partially embedded in the brazing material. This forms a layer of hard particles, with one side of the particles adjacent to the steel base plate, and with the other side of the hard particles forming a rough, angular surface, in which the hard particles are firmly bound by the brazing material. The next step is allowing the steel base plate, the hard particles and the brazing material to cool. When cooled, a drill resistant surface is the result. The drill resistant surface of the invention has exposed angular particles, which are the partially exposed hard particles, bound in a hard matrix. Because the surface is rough and it is formed of angular particles, there is no flat surface to serve as a starting point for a drill bit, thus when a drill is pressed into the rough surface, it can find no purchase, and this causes it to xe2x80x9cwalkxe2x80x9d. While it is xe2x80x9cwalkingxe2x80x9d and turning, the drill bit is likely to encounter the sharp edges and corners of the hard particles, which will catch the drill bit and cause it to break.
One way of constructing the drill resistant hard plate is so that the layer of hard particles is a monolayer, and is generally one particle in depth. The hard particles can be applied using a brazing rod containing the hard particles and a first brazing material, and using a second brazing material to help bind the hard particles and the first brazing material to the steel base plate. The second brazing material melts under applied heat, and forms a matrix binding the hard particles to the steel base plate and the first brazing material. In this way, the first and second brazing material blend together to form the matrix, and the matrix binds the hard particles, and may partially cover them. The hard particles can be one thirty-second to one-half inch ({fraction (1/32)}-xc2xdxe2x80x3) in thickness, but other thickness such as one-sixteenth to one-quarter inch ({fraction (1/16)}-xc2xcxe2x80x3) thick have also been found to be suitable. A thickness of approximately one-eighth inch (xe2x85x9xe2x80x3) has proven to be an optimal thickness for the layer of hard particles. The optimal size of the hard particles is related to the size of the drill bit to be defeated.
The hard particles can be made from a variety of substances such as tungsten carbide, titanium nitride, tantalum carbide, zirconium carbide, alumina, beryllium carbide, titanium carbide, silicon carbide, aluminum boride, or boron carbide. The hard particles can be from twenty-four (24) to six (6) mesh in size, and an optimum range is eighteen (18) to ten (10) mesh in size.
The first brazing material can be from a number of substances, but a suitable one is a nickel-copper zinc brazing material. One acceptable combination of these elements for a brazing rod is the combination of approximately ten percent (10%) nickel, forty-eight percent (48%) copper, and forty-two percent (42%) zinc. The second brazing material, which comprises the rod in which hard particles are delivered to the steel base plate, is nickel silver.
The invention also includes the drill resistant hard plate itself, separate from the method of making the hard plate. The drill resistant hard plate comprises a steel base plate, which serves as a support for the drill resistant hard plate. On one side of the steel base plate is located an anti-drill layer, which has an outward facing surface. The anti-drill layer is bonded to the steel base plate by epoxy, brazing material, or other binding material. The anti-drill layer comprises a layer or monolayer of hard particles which are attached to the steel base plate, and in which at least some of the particles are in contact with the steel base plate on one side, and in which the hard particles are at least partially exposed on the outward facing surface of the anti-drill layer. The outward facing surface of the anti-drill layer has an angular and uneven texture due to protrusion of the hard particles. This makes the outward facing surface a drill resistant surface with angular particles. Because of the angularity of the surface, there is no flat area for a drill bit to start in. For that reason, a drill bit xe2x80x9cwalksxe2x80x9d and chatters on the surface, and eventually encounters a sharp corner or edge of one of the hard particles, which catches the fluting of the drill bit and causes it to break.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.